Process for the recovery of hydrocyanic acid



Patented Oct. 28, 1941 2,266,881 'rnn nncovnar or armocrAmo ncm Helmut Beler, Frankfort-on-the-Mai'n, Germany,

assignonto Deutsche Gold and Silber Scheldeanstalt, Frankfort-on-the-Main, Germany, a corporation of Germany No Drawing. Application September 23, 1938,

Serial No. 231,327. In Germany April 11,

I'he object of the present invention is a process for recovering hydrocyanic acid "from thiocyanates, which comprises that aqueous solutions of alkali thiocyanates, as sodium thiocyanate, po-

platinumgauze, cathodes of graphite and anodes of magnetite may be used with special advantage. The process can be carried out with andwithout diaphragms. In usingaiiaphragms 4 Claims. (Cl. MIL-1,03)

be so chosen that they permit a rapid passage of the electrolyte and consequently a good exchange between catholyte and anolyte and that the smallest possible electrode interval be chosen.

tasslum cyanate, ammonium thiocyangt a d 5 However, it has proved more advantageous to h like. aresubiected to electrolysis, whereby work in cells without diaphragms. Expediently, Perhaps the Q' reactions may be allowed cells are used which contain'a plurality of electo take Place: the anodically evolved oxygen ortrodes united to an electrode system. the 8110mm? formed y gen peroxide oxidizes For carrying out the process current densities the ey ogen radical, whereby on of approximately '7 to 10 amp/dm. generally one hand. yd oeyanic acid is formed, while on have proved most favorable. In working up liqthe other hand, the free sulfur obtained from the uors whichcontain in addition to thiocyanates, mey nogen compounds is converted into sulfate larger or smaller amounts of thiosuliates or sulblsulfetefltes, as 'e. g. the thiocyanate liquors resulting in The i g conditions are to bechosen corr the coke and lignite industries, higher current 18 tothese r a ti ns, at is,insuch away densities, e. g. those up to 15 amp./dm. and that the oxidationproducts formed at the anode more can be chosen. The voltage may be e. g. can react in the best manner possible on th 5 to 10 volts. thiocyanate or its conversion products. More- The most suitable working conditions can be Over. it is practicable to prevent the free cyano- 2n ascertained by simple preliminary experiments. 86 r d l Obtained at the. anode from poly- On account of the formation of sulfate or bi- Y merizing to pseudothiocyanogen. sulfate the solution becomes acid in th electrol- 111 rr in out the electrolysis, the electrolyte ysis and the hydrocyanic acid formed is caused is heated to temperatures above room temperato escape from the warm acid solution. For proture' preferably to boiling temperatures. By moting the formation and the separation of the measures. h as thorough stirring, working hydrocyanic acid as well as for increasing the with small electrode intervals, expediently by conductivity of the solution, it is recommended 1181118 ve al Such measures, the process may be to acidity the electrolyte at the beginning of the influenced favorably in the above named sense. electrolysis. As acidifying agent bisulfate 0r sul- The undesired formation and separation of yelfuric acid may be usedadvantageously, although low pseudo thiocy'anogen at the anode can be obviously other acidic materials are likewise suitprevented by a suitable thiocyanate concentraabletlon of the y es. Advantageously liquors In order to keep the electrolyte at the desired are used which are less than approximately 0.6 thiocyanate concentration, it is expedient 'to innormal, e. g. 0.4 to 0.5 normal, in cyanate, In 5 troduce into the process continuously or disconworking up ammonium thiocyanate excellent retinuously concentrated thiocyanate liquor, e. g. suits are obtained in working up liquors which -liquors resulting in industry, whose thiocyanate contain approximately 40 to 50 g. ammonium concentration is, for the most part, a multiple thiocyanate per liter. In working up technical of e. g. ten times the concentration desired for crude liquors it has been found that higher thio- 40 the electrolysis, e. g. so that the concentration cyanate concentrations than those stated above of thiocyanate in the electrolyte is kept condo not in generalcause diiliculties. stantly at approximately the same amount, e. g.

The electrolysis can be carried out by direct 0.5 normal. current, alternating current, fluctuating direct In case of fresh electrolyte mixtures, it has current, or direct current with superimposed albeen found that generally about /2 to 1 hour ternating current. The above mentioned measelapses before the hy r y 1 yield r che ures, such as thorough stirring and working with its most favorable amount. on this basis, it is small electrode intervals have been shown to be recommended to begin the addition of more conexpedient 'especiallyinusingdirect current. The centrated fresh electrolytes only about $5 to 1 electrodes may consist e. g. .of platinuni,suitably hour after the beginning of the electrolysis.

Since the volumeof the electrolyte gradually increases by the addition' of fresh thiocyanate liqthe active electrode surface increases, it is rec- :it is recommended that the porosity of the same 5 amended to increase correspondingly the addition or energy so that the current density is kept as constant as possible. 4

The invention permits the obtaining of hydrocyanic acid and by-products in practically quantitative yields by a simple and easily carried out process; it offers among other things the advantage oif making inexpensive raw materials useful, especially the inexpensive thiocyanate liquors resulting on a large scale, e. g. in the gas Example 1 An aqueous solution which contains about 0.2 normal potassium thiocyanate is electrolyzed with platinum gauze electrodes at boiling temperature with direct current. The current den sity is about 9 amp/dim; the voltage between the electrodes approximately 8 to 9 volts. The electrolyte is slightly acidified with bisuliate before beginning the electrolysis. Iivdrocyanic acid which escapes as a gas, is formed immediate- 1y after starting the electrolysis. The escaping hydrocyanic acid can bee. g. liquefied by cooling or e. g. converted into alkali cyanide by absorption in alkali solutions with cooling. The bisuliate formed in the electrolyte can be obtained by the usual measures, e. g. by evaporating the electrolyte. The yield in hydrocyanic acid and bisuliate, calculated on the thiocyanate used, is practically 100%. Small traces of hydrogen sulfide. which possibly escape with the hydrocyanic acid can be separated by the usual methods, e. g. by washing or absorption of the hydrocyanic acid.

Example 2 I of magnetite.

The solution is heated to 98-100 and electrolyzed for 30 minutes with a voltage of to 6 volts and a current density of 15 amp/dm. Alter this-running time" the continuous addition of undiluted crude liquor begins, i. e. in such a way industry.

that 100 liters of crude liquor with a content of 55.48 kg. NH4CN8 are added in the course oi 5 hours.

The hydrocyanic acid evolved is liquefied by a known method. Aiter a total of 8 hours, 81.17

kL'NHiCNS of the 83.22 kg. NH4CNS- are decom-' posed and thus 22.57 kg. of liquid hydrocyanic acid are obtained. The residual liquor remaining in the electrolytic vessel contains L kg. K112411804. Thiscanbeusediordilutingthe thiocyanate crude liquor imtil the concentration 01' bisuliate becomes so high that the latter precipitates. The electrolysis is carried out eiilcient lyuntilallof the teis decomposed and the bisulfate is obtained by evaporation oi the liquor.

I claim:

1. A process for the production oi hydrocyanic 7 acid comprising electrolyzing an acidic aqueous solution of alkali thiocyanate containing less than about 0.6 normal alkali thiocyanate at a current density of approximately 7 to -15 amp./dm. while heating said solution substantially to its boiling point.

2. A process for the production of hydrocyanic acid comprising electrolyzing an aqueous solution of an alkali thiocyanate containing less than about 0.6 normal alkali thiocyanate, while'heating said solution to a temperature ranging from substantially above that resulting from themsage oi the electric current through the solution to the boiling point of said solution, and abide maintaining the reactants in intimate con- 3, A process according to claim zlwhereinintimate contact of the reactants is maintained by thorough'stlrring.

4. Aprocess for the production of hydrocyanic tact.

HEIMUT BEIER.

Patent Nb. 2,260,881.

cEmim'cAi' OF con-atom; 7

"BELHUT 33:11:12;

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